The present invention relates to an electronically controlled microwave phase shifter.
There exist today several types of phase shifters permitting the control of phase variations in a microwave signal. Known phase shifters include diode phase shifters and ferrite phase shifters which work by the modification of magnetic permeability.
Diode phase shifters typically present a fundamental inconvenience in that the minimum difference between two phase values such shifters are able to obtain remains high. Typically, for technological reasons and cost, the minimum difference is greater than 22.5 degrees. In order to diminish this minimum difference, it would of course be possible to increase the number of diodes in the phase shifter, but this would lead, on the other hand, to inadmissible energy losses and to operation which is limited to a very narrow band of frequencies. Furthermore, diode phase shifters require the use of components of very advanced technology and of high costs especially when one wishes to operate above 8000 MHz.
Theoretically, ferrite phase shifters allow for continuous variation of the phase of a microwave signal. Practically, they permit all useful phase variations (up to 5 degrees) in present industrial applications. Nevertheless they present a number of inconveniences, arising from their principles of operation, namely: (a) complexity of drive circuitry necessary for the production of the variable magnetic field, (b) large switching time, and (c) non-reciprocity between transmission and reception. Furthermore, the reversibility of such systems has a high reversibility time of the order of 1 millisecond. Other inconveniences are caused by the use of ferrites which provoke burdensome problems of weight and problems of instability with temperature since the operation of ferrite depends on the ambient temperature or the temperature resulting from the microwave energy passed through them.
It is, therefore, an object of this invention to provide a phase shifter of continuous or pseudo-continuous phase variation, which permits, as one will see, the avoidance of the inconveniences of known phase shifters.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.